1. Field of the Invention
The present invention relates generally to agricultural and industrial ventilation fans. More particularly, my invention relates to low-vibration ventilation fans of the type comprising fan blades that are directly connected to the drive motor.
2. Description of the Prior Art
It has long been recognized in the fan arts that moving air may be conveniently used to ventilate an area while simultaneously cooling it. A variety of fans are used extensively in agricultural facilities, especially in the poultry and dairy industries, to provide both ventilation and cooling.
To practically control the effects of wind or air cooling, it is desirable to control the direction, velocity, and volume of the air being driven. I have previously proposed a fan adept at controlling air over long ranges. My previous invention, issued as U.S. Pat. No. 5,480,282, on Jan. 2, 1996, and its teachings are hereby incorporated by reference. It was classified in U.S. Class 415, subclass 125. As can be seen from that patent and the prior art therein, the known prior art comprises many different types and designs of fans adapted to satisfy various criteria.
In the prior art it has been required to mount fans relatively close to the area to be cooled because the velocity of the expelled air drops dramatically as it leaves the fan. When expelled air leaves typical fans, extreme turbulence generated by the fan causes the expelled air to mix with surrounding air. The intermixing of the expelled air with the ambient air surrounding the fan results in a drop in volume, speed and pressure of the expelled air. This phenomena requires that the fan be mounted relatively close to the application it is to cool. It is often difficult to mount the fan as close as required to the application, in part because industrial-quality drive motors are very heavy, and the influence of vibration and extreme loads on the drive-train tends to degrade or loosen structural mounting parts over time.
To maximize the distance in which the fan will operate, the air must be concentrated and delivered properly for maximum effect. Concurrently, the fan must be properly mounted upon a suitable structure. It is also desirable to prevent workers from inadvertently contacting the fan, to avoid both mechanical and electrical injury. It is generally prohibited to mount fans with extension cords and other exposed electrical wiring.
Most industrial designs use a rectangular housing enclosing a multi-bladed fan that is belt driven at relatively high velocity. Such "tube axle" designs have several advantages. They are durable and rugged. They are relatively uncomplicated and easy to build. However, such fans can be noisy and they tend to vibrate, with vibration intensity often increasing over time. Loud, continuous rattles are annoying and distracting. Further, vibration can eventually loosen critical parts causing misalignment or premature breakdown. The long term structural durability of such fans is of paramount importance.
One cause of fan vibration relates to the "V-belts" or drive belts. In such fans the blade tip speed must be less than approximately one hundred miles per hour to minimize noise. Typically the fan speed is reduced from the motor speed by a ratio of three to one. This gear reduction results from the pulleys of various sizes connected by the V-belt. Over time typical V-belts will eventually wear and deform. Thereafter the tension transmitted by the belt between the axis of rotation of the fan blades and the drive motor axis will vary in response to rotation. An annoying oscillating effect can result. Unwanted vibration causes fan shaking and noise. Direct drive motors may ameliorate the problem of worn or distorted drive belts, and they reduce vibration and noise. But the motors in direct drive fans can be difficult to mount.
Another vexatious problem with conventional industrial fans involves structural deformation. Over time, internal stresses and dynamic forces generated during normal operation can misshape the fan, distorting the housing from the optimum round cross section. Many industrial fans are roughly moved about as necessary for spot cooling. Often these fans are mishandled, dropped, or subjected to other damaging forces through carelessness and the like. Known prior art fans are not designed to maximize structural strength. They fail to adequately compensate for stresses exerted by the motors and other internal components upon the housing during movement. Their guards fail to make a maximum contribution to structural integrity.
Finally, a problem with conventional fan housings involves the numbers of components that must be handled during assembly and maintenance. Conventional guards and guard attachment devices require handling and installing several parts during manufacture as well as removing a corresponding number during routine maintenance. Also, most conventional mounting brackets use several components pieces that require considerable assembly time. Such brackets are often difficult to handle and store.
The trend toward direct drive fans and their inherent simplicity has been the driving force to improve motors and their application to ventilating fans. In a direct drive ventilation fan the fan blades are rotated through direct contact with the drive motor. These direct drive motors turn at a slower speed than motors in conventional belt drive systems. For example, to obtain the correct blade speed for a 36 inch fan the direct drive motor need only turn 850 RPM. The conventional belt-driven fan, comprising a conventional capacitor start motor turning approximately 1750 RPM, requires two pulleys to divide the fan speed range down to approximately 500-800 RPM. Direct drive systems eliminate the complex speed reduction system. This greatly reduces the vibration and noise associated with conventional belt and pulley systems.
Conventional systems for mounting motors and engines has evolved around the need to support the center of the torque moment. In many industries large engines have mounting arrangements that isolate vibration and control torque with circular placement of isolation points. In some cases, several isolation mounts are located in a circular pattern to maintain shaft alignment and absorb torsional shock.
Small electric motors are available with concentric elastomeric mounting on each end of the motor to maintain concentricity and isolate vibration. Many mounting bases are offered as add-on isolation and belt-tensioners but do not maintain concentricity. Base mounted isolators by their very shape are unstable and allow harmonic movement, rendering them undesirable for close tolerance fan applications. Motor mounting for perfect concentricity and rigidity is well accomplished with the "C" face mounting. The "C" face motor requires an adapter plate to complete a mounting system for a fan. Any plate used for mounting also acts as an air deflector and causes turbulence that reduces the cooling effect of the air flow.
When motors are used to directly drive a fan blade it is desirable to have an unobstructed flow of air over the motor. Some fans have add-on flat mounting strips and lugs that allow attachment of flat plates which extend to the fan housing. These strips are mounted parallel with the air flow and obstruct the flow very little. Flat strips, however, and similar mounting methods tend to vibrate more than most arrangements. This type of mounting system must be limited to small motors.
Thus it is desirable to provide a fan with a highly efficient direct drive motor and a cooperating mounting system that provides a rigid support near the center line of the mass of the motor. Also it is desirable that the free flow of air over the motor housing be unobstructed.